I did Half-Dome over the July 4th Weekend for my first time, and good on ya for wanting to train. Here's what I did to train:
The thursday before leaving, I hiked the Skyline to the Sea trail in Big Basin - the hike we did to Berry Falls was about 11 miles roundtrip and coming back on the Howard King trail we had a 1300 ft elevation change. That was an asskicker.

In early May, we did a reverse-Bay2Breakers. Started at the Sutro Baths at the end of Geary, and hiked out to Land's end, then along the ocean in Seacliff, down to Baker Beach, back up to Lincoln (I believe) through the Presidio, and eventually over to the Fisherman's Wharf for dinner. We started late and it got dark on the way back, so we took a cab back to the car. That was a good 8-mile walk that covered a lot of the city and a lot of terrain.

Twice in June I hiked up Mt Tam - both times we started near the Mountain Theater. The first trip we hiked to the North Peak, and the second was just a jaunt around the hills looking for a special grotto that didn't seem to be there anymore. Both hikes had good elevation gain, tho and lasted 3-5 hours.

I've heard that the Dipsy trail is great, too. That's on my list for next week.

sport drinking. i drank beer all day friday and road soda-ed it to yosemite friday evening. we woke up bright and early sat to hike half dome. everyone said i wouldn't last, but i did just fine. i play a lot of sports though and hike on a regular basis. athletic alcoholic...it works for me :)

oh...and goo....bring a few packets of goo and slurp it down during the hike.

If you work in Sausalito, try hiking up Mt Tam after work. Follow the route used in the yearly DipSea Race. Start in downtown Mill Valley and walk through the park on the west side of town and follow the 400+ steps up, cross the road and proceed into open space. It's about 5 miles to the top. I'd bet many of the local shop owners would know the route; ask them. Do some exercise daily and Half Dome should be easy. A camelback, one that has room for snacks, small flashlight, and a light jacket, would be a great item to have on your trip. Half Dome is a great hike.

One- Mission Peak in Fremont. This is a butt-kicker, literally. Your butt and groin will feel awesome! lol it's about 7.5 miles RT with about 2200+ elevation gain/loss. There are many trails here, but be prepared for hot weather. this one is really best in winter/early spring or early morning.

Two- Try Big Basin Berry Creek Falls. Actually there is a group going this Sunday. but they are going in from Waddell creek. Roughly 13-15 miles RT. Not sure elevation. You can also do this from the headquarters, which I have done recently for a 11-12 mile RT hike.

Three- In the South Bay, Sierra Azul Kennedy Trail. Los Gatos. This will kick you in the butt as well. It's about a 8 mile RT hike w/ 2000+ elevation gain/loss. A lot of mtn bikers go here as well. It does get pretty hot here so be prepared.

Four- Oh another good one, which I have done recently as well, is Muir Woods. Headquarters to Stinson Beach!! I think if you did this RT it would be 14+ miles. Well, lets just say we didnt do the RT we did the one way and took the bus back. lol If you can handle the million people in the summer, then all is good.

Also check out Tom Stienstra's California Hiking book. Excellent man and knowledge for alot of adventures.